1. Technical Field of the Invention
This invention relates to a liquid crystal display device that has a pair of substrates and a liquid crystal layer as an optical modulating layer therebetween, and a method of driving the same.
2. Discription of the Related Art
In recent years, taking advantage of their thinness, light weight and low power consumption, liquid crystal display devices have been used in various fields as display devices for personal computers, word processors, and also as projection type display devices.
Active matrix type display devices having pixel electrodes, each of which is connected with a switching element respectively, can realize an excellent display image without crosstalk between adjacent display pixels, and have been studied and developed vigorously.
Herein after, it will be briefly explained that a construction, for instance, of a light transmission type active matrix liquid crystal display device. This liquid crystal display device provides an array substrate, a counter substrate, a liquid crystal layer coupled with alignment layers on each substrates.
The array substrate, for instance, provides a plurality of signal and scanning lines in a matrix form, thin film transistors (TFTs) as a switching element formed at the vicinity of each crossing points thereof, and pixel electrodes made of I.T.O.(Indium Tin Oxide) connected with the switching elements on a glass substrate.
The counter substrate provides a light shielding layer formed on a glass substrate so as to shield a light passing through peripheral areas of pixel electrodes and a light irradiating toward the TFTs, and a counter electrode made of I.T.O. and formed on the light shielding layer via an insulating layer.
Now, regarding to each display pixels of this liquid crystal display device, a pixel electrode potential (Ve) of the display pixel changes under the influence of a leak current through the TFT and parasitic capacities of the TFT. Therefor, it is necessary to provide a storage capacitor (Cs) parallel to the liquid crystal capacity (Clc) so as to reduce the pixel electrode potential change, and the following two structures are well known.
The first structure is that the storage capacitors (Cs) are constructed with storage capacitor lines arranged in parallel with the scanning lines on the grass substrate of the array substrate, the pixel electrodes of which a part is overlapped with the storage capacitor lines respectively, and an insulating layer formed therebetween.
The second structure is that the storage capacitors (Cs) are constructed with the scanning lines, the pixel electrodes of which a part is overlapped with the neighboring scanning lines, and an insulating layer formed therebetween.
The second structure has an advantage to realize a high aperture ratio comparing to the first structure because of its arrangement without the independent storage capacitor lines.
In the liquid crystal display device mentioned above, it has been known that reverse image regions, which can not be controlled to the normal display state, have occurred in area where lateral electric fields between electrodes on the array substrate are against a pre-tilt direction of liquid crystal molecules, and the liquid crystal molecules are aligned along with the lateral electric fields.
In FIG. 7, 103, 111, 121, and 151 indicate signal lines, scanning lines, and TFTs, respectively. A solid and dot arrow lines indicate rubbing treatment directions of alignment layers on the array and counter substrates, respectively. And a twisted nematic (TN) liquid crystal layer including liquid crystal molecules is held between the substrates and the liquid crystal molecules is twisted at 90 degrees between the substrates.
The lateral electric fields which are against the pre-tilt direction of the liquid crystal molecules have occurred between the pixel electrodes 151, and the signal and scanning lines 103 and 111 and the pixel electrode 151 adjacent thereto, and an oblique line region in this Figure becomes a reverse image region.
It will be understood by this Figure that the reverse image region may extend in the pixel electrode 151 in accordance with an intensity of the lateral electric fields.
To eliminate the occurrence of the reverse image regions, it has been known that a liquid crystal display device, for instance, provides the scanning lines each of which comprises an extended portion extended between the signal line and pixel electrode electrically shielding the lateral electric field generated therebetween.
The inventors have newly found out by their own study and investigation that the occurrence of the reverse image regions can not be eliminated, even if the structure mentioned above is introduced.